Methods and systems for scheduling work

• US 6,684,117 B2
• Filed: 05/02/2003
• Issued: 01/27/2004
• Est. Priority Date: 03/31/2000
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Ribeiro, Wesley Elias, Nogueira de Meneses, Claudio, Sergio de Souza, Pedro, Bacin, Edson, Macedo, Ivan Roquete
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): Bahta, Kidest
• Application Number:
  US10/428,478
• Publication Number:
  US 20030195648A1
• Time in Patent Office: 270 Days
• Field of Search: 700/99-100, 700/106, 700/115, 700/107, 700/109, 705/7-10, 705/11, 705/28
• US Class Current: 700/98
• CPC Class Codes: B21B 1/00 Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section B21B17/00 - B21B23/00 take precedence; with respect to composition of material to be rolled B21B3/00; extending closed shapes of metal bands by simultaneous rolling at two or more zones B21B5/00; metal-rolling stands as units B21B13/00; continuous casting into moulds having walls formed by moving rolls B22D11/06; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
• CPC Class Codes: B21B 37/00 Control devices or methods specially adapted for metal-rolling mills or the work produced thereby methods or devices for measuring specially adapted for metal-rolling mills B21B38/00
• CPC Class Codes: G05B 19/41865 characterised by job scheduling, process planning, material flow
• CPC Class Codes: G05B 2219/32256 Due dates, pieces must be ready, priority of dates, deadline
• CPC Class Codes: G06Q 10/06 Resources, workflows, human or project management; Enterprise or organisation planning; Enterprise or organisation modelling
• CPC Class Codes: G06Q 10/087 Inventory or stock management, e.g. order filling, procurement or balancing against orders
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

Abstract

In a first aspect, the present invention provides a unique algorithm that interactively takes into consideration the melt shot (MS) and the hot strip mill (HSM) constraints such that a balanced and feasible solution is reached for the whole Primary Area (MS and HSM) at once. In a second aspect, the invention takes a set of orders defined to be produced next in the Melt Shop area in a steel mill and groups them in small sets of orders with similar characteristics, called heats. Each order belongs to a heat. The system defines the precise moment that each heat has to be processed in each of its steps. In another aspect, the invention uses an event-driven based algorithm as a general approach for scheduling all the processing units with their specific constraints and the metallic units from hot coils to the finished products at the shipping areas.

Claims

1. A system for scheduling operations in a steel mill, comprising:

means for reading all the orders that must be produced in a certain period of time and for creating the necessary number of slabs to satisfy the orders;

means for reading all the virtual slabs to be produced and their due dates as hot coils, and for generating an ideal rolling sequence of slabs;

means for reading an ideal rolling sequence of slabs and for generating a set of heats to be produced;

means for reading the real slabs to be produced, for generating a plurality of hot coil schedules, and for writing hot coil schedules into a hot coil schedule memory;

means for reading a plurality of solutions from the hot coil schedule memory, for extracting common parts from the plurality of solutions, and for using the extracted parts as an initial partial solution for a hot strip mill sequencing algorithm.

2. A system according to claim 1, wherein the means for reading all the orders includes means for generating an output identifying the number of slabs to be produced and their specifications.

3. A method for scheduling operations in a steel mill, comprising the steps:

reading all the orders that must be produced in a certain period of time, and creating the necessary number of slabs to satisfy the orders;

reading all the virtual slabs to be produced and their due dates as hot coils, and generating an ideal rolling sequence of slabs;

reading an ideal rolling sequence of slabs and generating a set of heats to be produced;

reading the real slabs to be produced, generating a plurality of hot coil schedules, and writing hot coil schedules into a hot coil schedule memory; and

reading a plurality of solutions from the hot coil schedule memory, extracting common parts from the plurality of solutions, and using the extracted parts as an initial partial solution for a hot strip mill sequencing algorithm.

4. A method according to claim 3, wherein the step of reading all the orders includes generating an output identifying the number of slabs to be produced and their specifications.

5. A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for scheduling operations in a steel mill, the method steps comprising:

reading all the orders that must be produced in a certain period of time and creating the necessary number of slabs to satisfy the orders;

reading all the virtual slabs to be produced and their due dates as hot coils, and generating an ideal rolling sequence of slabs;

reading an ideal rolling sequence of slabs and generating a set of heats to be produced;

reading the real slabs to be produced, generating a plurality of hot coil schedules, and writing hot coil schedules into a hot coil schedule memory;

reading a plurality of solutions from the hot coil schedule memory, extracting common parts from the plurality of solutions, and using the extracted parts as an initial partial solution for a hot strip mill sequencing algorithm.

6. A program storage device according to claim 5, wherein the step of reading all the orders includes generating an output identifying the number of slids to be produced and their specifications.

7. A system for scheduling work orders in a plant, comprising:

means for grouping the orders into heats;

means for creating a reference list for the heats, from which the heats are pulled to be scheduled;

means for identify current plant conditions;

means for testing a best value of an objective function for taking B possible schedules of heats, where B is an internal parameter;

means for forming sequences of up to P heats to be scheduled in order, where P is an internal parameter;

means for identifying the best of said sequences, without any re-arranging of the heats, and fixing the first heat of the best sequence as scheduled, after testing a number of possibilities; and

means for removing the fixed heat from the reference list.

8. A system according to claim 7, wherein said number of possibilities is approximately B^p.

9. A system according to claim 7, wherein each heat is provided with a route that describes the production steps that the heat has to go through.

10. A method for scheduling work orders in a plant, comprising the steps:

grouping the orders into heats;

creating a reference list for the heats, from which the heats are pulled to be scheduled;

identifying current plant conditions;

testing a best value of an objective function for taking B possible schedules of heats, where B is an internal parameter;

forming sequences of up to P heats, where P is an internal parameter;

identifying the best of said sequences and fixing the first heat of the sequence as scheduled, after testing a number of possibilities; and

removing the fixed heat from the reference list.

11. A method according to claim 10, wherein said number of possibilities is approximately B^p.

12. A method according to claim 11, wherein each heat is provided with a route that describes the production steps that the heat has to go through.

13. A method for scheduling production processes in a plant, comprising the steps:

a) reading information regarding what the plant has done, and the situation of metallic units and processing units in the plant;

b) identifying what each processing unit will be doing with the metallic units;

c) reading the next step to be executed in the route assigned to each metallic unit;

d) assigning a virtual time indicator and increasing the virtual time until a metallic unit is released by a processing unit;

e) checking the next routing step of the metallic unit, and placing the metallic unit in the set of the processing units that can execute the step;

f) verifying if all the metallic units of the same type of the one just finished are complete;

g) if not all the metallic units are complete, then assigning the next metallic unit to the processing unit;

h) if all the metallic units are complete, then selecting, from among all the types of materials available for that processing unit, which one is the best type to go next;

i) defining the best order of the metallic units in the selected group;

j) assigning the first metallic unit to the processing unit; and

k) evaluating the processing time of said first metallic unit.

14. A method according to claim 13, further including the step of increasing the virtual time to the next event, and repeating steps (f) through (k).

15. A system for scheduling production processes in a plant, comprising means

means for reading information regarding what the plant has done, and the situation of metallic units and processing units in the plant;

means for identifying what each processing unit will be doing with the metallic units;

means for reading the next step to be executed in the route assigned to each metallic unit;

means for assigning a virtual time indicator and increasing the virtual time until a metallic unit is released by a processing unit;

means for checking the next routing step of the metallic unit, and placing the metallic unit in the set of the processing units that can execute the step;

means for verifying if all the metallic units of the same type of the one just finished are complete;

means for assigning the next metallic unit to the processing unit if not all the metallic units are complete;

means for selecting, from among all the types of materials available for that processing unit, which one is the best type to go next, if all the metallic units are complete;

means for defining the best order of the metallic units in the selected group;

means for assigning the first metallic unit to the processing unit; and

means for evaluating the processing time of said first metallic unit.

16. A system according to claim 15, wherein the means for reading the next step to be executed include means for replicating the metallic units in the set of each processing unit that can execute the step.

17. A method for scheduling work in a hot strip mill, comprising the steps:

establishing conditions for all processing units in the host strip mill area and fir the available slabs in stock;

group the slabs with similar routes, and identifying the critical sequences for each route;

evaluating the buffer size of be last step of a non-critical sequence so that a minimum lot size is reached before starting a critical sequence;

selecting slabs to be assigned to the buffers;

scheduling slabs for the processing units in the non-critical and in the critical sequences; and

if a conflict is detected, delaying the processing starting time of buffer to eliminate the conflict.

18. A method according to claim 17, wherein a critical sequence is a sequence of operations that has no wait time in-between any two operations of the sequence.

19. A system for scheduling work in a hot strip mill, comprising:

means for establishing conditions for all processing units in the host strip mill area and for the available slabs in stock;

means for grouping the slabs with similar routes, and for identifying the critical sequences for each route;

means for evaluating the buffer size of the last step of a non-critical sequence so that a minimum lot size is reached before starting a critical sequence;

means for selecting slabs to be assigned to the buffers;

means for scheduling slabs for the processing units in the non-critical and in the critical sequences; and

means for delaying the processing starting time of buffer, if a conflict is detected, to eliminate the conflict.

20. A system according to claim 19, further comprising means for providing starting and finishing times that each slab is processed in each processing unit of its route.